Photovoltaics of the Future: A Potential New Energy Source

By on March 11, 2014

The prospects of a new device that can absorb infrared emissions from the Earth and convert it into useful energy has been proposed by researchers at the Harvard School of Engineering and Applied Sciences.

When sunlight strikes the Earth’s surface, some light is reflected back into space, while the rest is absorbed into the Earth itself. Like the sun emitting solar radiation, the Earth emits its own infrared radiation, or heat radiation, into its atmosphere, effectively warming the planet. This is where the greenhouse effect emerges; gases in the atmosphere trap the heat.

Researchers decided that, however unconventional it may be to harvest energy from the Earth’s own radiation, there may be significant economic and scientific gains should the technology emerge. For one, this device could potentially be used with solar panels so that energy can be harvested day and night—something that solar panels on their own cannot do. In fact, in one of the two designs the researchers proposed, the device was modeled after the photovoltaic cell.

Photovoltaic cells, which make up solar panels, utilize the photoelectric effect as discovered by Albert Einstein. One cell is made of a semiconductor wafer that is specially treated to be charged positively on one side and charged negatively on the other. When light strikes the cell, electrons are knocked off the wafer. These electrons, with the help of conductors on both sides of the wafer, form a current, which is electricity.

The researchers proposed two different models of this new device—a macro- and a micro-scale model. Similar to how the solar cell takes advantage in the difference between positive and negative charges, the macro-scale model would be two plates, one cold and one hot. The cold plate, made of some material that could reflect enough light to keep itself properly cool, would lie on top of the hot plate, and this difference in temperature would generate work—or energy. As a case study in Oklahoma, they found that this method could generate a few watts per square meter. The trick now is to find a better material for the cold plate so that it will remain effectively cool throughout the day and night.

The micro-scale model is more complicated, but relies on the same principle of temperature difference—except between nanoscale structures. It more specifically deals with diodes and resistors, components of electrical circuits. Basically, the diode must be a higher temperature than the resistor, which must efficiently emit the heat to stay cool. This temperature difference also elicits an electrical current.

One limitation to the micro-scale device is that diode technology may not be up to par with its demands; diodes that can deal with infrared emissions produce low voltage because infrared waves are comparably low in energy. So these researchers are looking into new materials or types of diodes to accommodate the demands.

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